227] STUDIES ON GREGARINES WATSON 17 



contents may be ten or more times the size of the normal epithelial cell ; 

 the parasite finally breaks out, for its rate of growth exceeds that of the 

 epithelial cell, whereupon the latter shrinks and finally disappears, the 

 adjoining cells gradually filling in the space left. The author says the 

 chemical substance secreted by the parasite at first stimulates growth in 

 the epithelial cell and later retards it, killing the cell, the parasite escap- 

 ing after dissolution has set in. The normal excretion must be emptied 

 into the cytoplasm of the epithelial cell of the host and may provoke 

 changes therein but whether or not the cell is killed by the entrance of 

 this foreign substance is a question. There is no other source of food for 

 the parasite than by absorption from the cell which surrounds it, and it 

 appears to the writer that the shrinking of the cell is due at least in part 

 to the gradual withdrawal of its liquid content and the absorption of the 

 latter by the contiguous parasite. How else the intercellular parasite 

 grows is not easily explained. If the host cell is killed by toxins which 

 are the excretory products of the parasite, the dead protoplasm is grad- 

 ually used up as food for the growing organism. An animal is generally 

 poisoned by its own excretory products ; the gregarine would seem to be 

 an exception unless it is possible that the host cell remains alive and 

 throws off the excretions of the parasite along with its own. 



Those parasites which are not intercellular possess epimerites by 

 which they are attached to the free end of the epithelium of the host, the 

 rest of the parasite lying in the lumen of the intestine. 



Five questions may be asked in this connection: (1) Does the epi- 

 merite absorb food from the parasitized epithelial cell? (2) Does the 

 epimerite absorb from the latter all the food that the gregarine receives ? 



(3) Does the epicyte of the gregarine body absorb all the food from the 

 lumen of the intestine, and the epimerite act only as a holdfast organ? 



(4) Is a toxic substance given out through the wall of the parasite into 

 the lumen of the intestine which is absorbed by the parts of the epithelial 

 cells nearest the surface? 



Laveran and Mesnil (1900) state that in Pyxinia frenzeli the cell to 

 which the parasite is attached at first greatly hypertrophies then atro- 

 phies and finally disappears completely about the time the cephalont is 

 ready to discard the epimerite and live free in the intestine. The hyper- 

 trophy, they say, is due to an increase in the liquid content of the cell 

 only, with a decrease in the density of its cytoplasm and nucleus. They 

 do not attempt to give an explanation for the cause of the phenomenon. 



Leger and Duboscq (1902) think this hypertrophy is only apparent 

 and not real, for the penetration of the sporozoite into the cell irritates it 

 so that the cell contracts in length at the same time increasing in width, 

 the latter phenomenon giving rise to the idea that there is hyertrophy. 

 They think the parasite absorbs the cell content through the epimerite 



